Fusible switches having a fuse and a current carrying blade utilize externally powered devices, such as relays or solenoids, to actuate the opening of the blade when the fuse blows due to an overload or short circuit condition. A problem could arise if the external power became unavailable when it was needed to operate the relay or solenoid for actuating the opening of the switch. Therefore, there is a distinct need to provide an assembly which utilizes only mechanical components to actuate the opening of the switch.
The use of interlocks to prevent closing the blade in a fusible switch after its fuse has blown is shown in German pat. no. DE 31 12295 A1. However, interlocks in the prior art only prevent closure of the phase that the fuse and switch are associated with. A need therefore exists for utilizing an interlock assembly for preventing closure of all three phases in a three phase fusible switch. Additionally, some interlock assemblies in the prior art require electrical power to operate external devices, such as solenoids and relays, for preventing the blade of the switch from being closed after the fuse has blown. Therefore, there is a need to provide an interlock assembly that does not require external power to prevent the switch from closing.
Additionally, when a fuse in a single phase of a multi-phase fusible switch blows and the other phases continue to conduct electrical current, a single phase condition exists that may damage the electrical equipment that is downstream from the switch. Accordingly, in order to prevent a single phase condition, there is a need for providing an interlock assembly for actuating the opening of all of the phases in a multi-phase fusible switch in the event that any one of the fuses blow.